Method of preventing pressure strains on invested articles during molding



Jan. 7, 1-941. Pi w LE 2,228,059

' METHOD OF PREVENTING PRESSURE STRAINS 0N INVESTED ARTICLES DURING MOLDING Filed Dec. 25, 1958 2 Sheets-She et 1 l 'i I i 1 6 I l l I I l I l l I l Fl IELE.

6s $2 J ix I 1 1V v I INVENTOR. Pyu/ve T00 [Wu/4H 55 A TTORPJ E Y.

BY 2 g I METHOD OF PREVENTING PRESSURE STRAINS ON INVESTED ARTICLES DURING MOLDING 2 Sheetsl-Sheet 2 P. W. LEE

Filed Dec. 23, 1958 FIG my r Jan. 7, 1941.

INVENTOR.

ATTORNEY.

Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE METHOD OF PREVENTING PRESSURE STRAINS ON INVESTED ARTICLES DUR- ING MOLDING Application December 23, 1938, Serial No. 247,483

1 Claim.

This invention relates to investments, and has special reference to a method and apparatus for investing articles whereby pressures caused by temperature changes are eliminated from the article per se.

In the investment of dentures or the like where the article to be treated is surrounded by investment material in a metal casing and the whole subjected to heat and pressure, and for vulcanizing, vitrifying or otherwise treating the article,

the relative contraction and expansion of the investment material and easing or flask during firing or cooling frequently exert pressures on the article being treated so that said article is sometimes distorted or strained and more frequently cracked and otherwise injured. Oitimes these imperfections in the denture itself are latent but invariably they result in eventual breakage.

The object of the present invention is to provide means to prevent excessive pressures upon articles during investment, and attendant heating and cooling.

A further object of the invention is to provide means which will permit a relative contraction and expansion of investment material and its casing or flask in an area remote from the article being invested.

A still further object of the invention is to provide means for more facilely removing investment material from the casing or flask.

According to the invention, a multiple-piece flask or casing, such as ordinarily employed for investment purposes, has its vertical walls provided with material which, upon the application r of heat, will permit the relative contraction and expansion of the investment material and easing or flask therebetween without imposing excessive pressure on the article being invested.

The drawings illustrate an embodiment of the invention and the views therein are as follows:

Figure 1 is a top plan viewof an improved investment flask or casing,

Figure 2 is a vertical sectional view taken on the line 2-2 of Figure 1 showing the flask or casing halves separated and with a lining of material around the vertical wall of each half,

Figure '3 is a view similar to Figure 2 showing the two halves of the flask or casing in cooperative position and with a denture model embodied in investment material in the lower hall of said flask or casing, said model having an article thereon to be invested,

Figure 4 is a view similar to Figure 3 showing the upper half of the flask or casing filled with investment material, and

Figure 5 is a like View showing the lining removed from the flask or casing.

The flask or casing shown in the drawings has an upper and lower part 6 and I. This type of flask is not the usual type, the latter being one in which the lower part I is substantially the same as that shown in Figure 2, while the upper part consists of a ring having a separate plate across the top. The flask here shown is provided with complementary internal enlargements 8, the upper half having pins 9 adapted to enter holes H in the lower half to center the halves together. The upper half has an opening I2 through which investmentv material is admitted to the inside of the flask, as later explained, and is also provided with a vent hole l3. Figure 2 shows a liner I4 extending entirely around the inside of the Vertical wall 16 of the upper half and a liner l'l extending entirely around the inside of the vertical wall l8 of the lower half.

This liner may be made of various materials, e. g. wax, asbestos paper or other easily compressible matter.

In Figure 3, a denture model I9 is shown embedded in investment material 2| in the lower half 1 of the flask, the liner l1 extending completely around between the investment material and the vertical wall of said half. On the denture model I9 is an article consisting of a denture or artificial tooth plate 22 comprising teeth 23 and denture base material 24. This denture base material may be resinous vulcanite, porcelain, glass or any material which is used as a base for holding the teeth and for fitting into the mouth of an edentulous person.

The investment material 2| is introduced into the bottom half of the flask in flowable or plastic form, and after the same is hardened the upper surface is provided with material 26 for preventing other investment material placed thereon from uniting with the investment material in the lower half of said flask. This material 26 may be merely a coat of varnish or other material painted or sprayed thereon, or may consist of a thin sheet of material, such as Cellophane or the like. After the investment material H is dry and set, the upper half 6 of the flask is applied, the pins 9 fitting into the holes I I, so that the vertical walls It and [8 of said halves are aligned. Investment material is then poured or otherwise introduced into the upper half of the flask through the opening I2, so as to fill said flask with the investment material 21. After the investment material 21 in the upper half of the flask is set, in some instances, the liners l4 and I! may be removed by separating the halves of the flask, and in case of wax, this may be washed out by the use of warm water, while other compounds will require a higher degree of heat to melt the strip or liner, after which, they can be poured out.

Where the strips or liners I4 and I1 are of easily compressible material, such as asbestos paper, cardboard or a loosely compacted fibrous compound, there will be no necessity for separating the halves of the flask, but the flask itself may be fired just as soon as the investment material in the upper half hardens. During the firing of the flask, the same is placed in a press so that pressure is applied to hold the flask halves and investment bodies tightly together.

It will readily be seen that in cases where the liners have been removed, and in any other cases where the liner is composed of readily compressible material, the relative forces or pressures caused by contraction and expansion of the metal flask parts and the investment materials will be absorbed either in the space formerly occupied by the liners or through the compression of the readily compressible material.

This invention has been tested and articles invested by this process have been found to give most satisfactory results free from both patent and latent defects, and not susceptible to ready breakage from pressures such as are inherent in the process of conventional investment.

The invention has the following advantages:

(a) It eliminates any pressure on the article by allowing free expansion of the investment compounds.

(b) It eliminates any pressure on the article by allowing free contraction of the investment compounds upon cooling without any squeezing by the faster contraction of the metal flask.

(c) It eliminates pressure on the article by allowing free contraction of the metal flask toward the investment compounds without pressing same against the article.

(d) It eliminates pressure on the investment which would be created by the expansion of the investment against the metal flask.

(c) It will eliminate the possibility of the investment compound materials sticking to the vertical walls of the flask.

While it has been mentioned that the lining may be composed of wax, cardboard or fibrous material, it will, of course, be understood that other entirely removable materials and other resilient or compressible materials may be employed, and hence the invention is not limited to any particular liner material.

Of course, with this in mind, the process and means for eliminating pressures on investments created by temperature changes may be modified in various ways without departing from the invention herein set forth and hereafter claimed.

The invention is hereby claimed as follows:

The process of molding articles by the use of a flask and an investment compound, comprising the lining of the aligning Walls of said flask with material which will burn out and provide space to allow free relative lateral contraction and expansion of said flask and investment material during heating and cooling of said flask.

P. WILLIAM LEE. 

